Wide band cavity type aerial



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E D I W oct. 3o, 1956 y United States Patent O WIDE BAND cAvrrY TYPE AERIAL Eric Osborne Willoughby, Glenunga, South Australia, Australia, assignor to Edwin William Hicks, Secretary of the Department of Air, Melbourne, Victoria, Aus'- tralia Application July 15, 1953, Serial No. 368,058

1 Claim. (Cl. 343-745) This invention relates to an improved cavity type aerial utilising a box in which the radiating member is disposed and to which the signal is fed and in the face of which box is a plurality of transmitting slots tuned progressively different by such an amount that between them they extend the effective frequency of operation. Thus instead of producing a narrow peak and thus a confined band Width each slot by being tuned to a slightly different resonant frequency will act with the others of the series to produce a plurality of overlapping peaks which results in a total signal of relatively greater overall band width than the comparable single slot aerial.

The effect of the system can best be appreciated if the radiating member is considered to have an inductance behind each slot which works into a tuned inductance formed by the slot immediately in front of it, the frequency of each slot being slightly transposed from the next slot so that although each tuned slot radiates on a relatively narrow wave-band, the collective effect is to produce a wider overall wave-length due to overlapping. Thus the wave emitted by the radiating member is spread by the separately tuned resonant slots.

The slots can themselves be tuned by condensers or other similar means, the radiating member and the transmission line being able to be tuned to the desired frequency by any known means.

The ends of the slots can be of key-hole type if such is desired and for normal purpose preferably three such slots are used in the face of the box, these slots being disposed parallel to each other and spaced slightly apart and being fed from the radiating member which is disposed transversely behind the slots. Alternatively a plurality of such boxes each having a tuned slot may form part of an aerial system with a suitable separation between the boxes, for instance a half wave length.

A radiating member constructed in this way produces an effective aerial system in which each of the slots may be sharply tuned to a frequency varying just slightly from its neighbour so that the collective effect of the slots is to give a material increase in the effective band width transmission due to the overlapping of the wave and the production of a compound frequency by means of which the desired band width is obtainable.

In order, however, that the nature of the invention may be more clearly understood it will now be described with reference to the accompanying drawings in which:

Fig. 1 shows one embodiment of the invention, the view being taken from the rear of the box with the back cover removed so as to show the slots, the feed member and the tuning members,

Fig. 2 is a sectional plan as online 2-2 of Fig. 1,

Fig. 3 is a view corresponding to Fig. 1 but showing a modied form of construction,

Fig. 4 is a plan of same as on line 4-4 of Fig. 3, and

Fig. 5 is a rear view of a further modification in which a pair of boxes with tuned slots are separated by, for instance, a half wave length.

Referring first to Figs. 1 and 2, the box is composed of a front 1 to f orm three cavities 2 with sides 3Z ends 4 and a back 5, the resonant cavities being of a size consistent with the frequency which irsgbeing fed to the System. l y g In the front 1 of the box are three slots 6 having cn"- cular cuts at the end to form as it were key hole slots 7 and across these slots are disposed three condensers 8 each having one member secured to the front 1 at a point 9 on one side of the slot 6 and the other member secured at a point 10 on the other side of the slot with which 1t is associated. In this way a change in capacity of these condensers will serve to tune the slots and by therefore tuning the slots to slightly different frequencies the desired effect which it is the object of this invention to obtain 1s achieved in that each slot will operate at a resonant frequency slightly different from its neighbouring slot.

The feed to the slots is by means of a strip 11 which is adjustably earthed at 12 to the bar 13 so that the strip can be moved up and down while the other end of the strip 11 has the signal fed thereto by a transmission line 14.

lIn the embodiment shown in Figs. 3 and 4 two separate resonant cavities 20 and 21 are formed, the box in this case comprising a front 22, a pair of side members 23, end members 24 and a back 25 but the box is further sub-divided by a central partition 26 which forms it into the two chambers 20 and 21.

A single slot 27 is centrally divided by a division 26 and tuning of the two parts of the slot so formed is obtained by a pair of condensers 28 one being connected across each of the two parts of the slot 27.

The feed to the slots is again effected by a strip 29 which is earthed at 30 to a bar 31 but is slidable thereon, while the feed to the strip 29 is by means of a transmission line 32 of any usual or approved construction.

In the embodiment shown in Fig. 5 two boxes 35 and 36 each has a slot designated respectively 37 and 38. The slots are tuned by condensers 39 and 40 across same, while the feed to the slot 37 is by a strip 41 and the feed to the slot 38 is by a strip 42. A transmission line 43 feeds the signal to the strip 42 and the strip is in series with a continuation 44 of the transmission line which connects it to one end of the strip 41 the other end of which is earthed at 45 to the face of the box 35. The boxes are preferably separated by half a wave length. More than two boxes could be used with suitably altered spacings, depending on how many tuned slots are desirable.

From the foregoing it will be appreciated that an aerial is provided in which slots having different tuning are provided in front of a resonant cavity or cavities but all of the slots are fed from a common source by means of the strips 11 or 29.

It will, however, be readily appreciated that the tuning of these slots can be varied by utilising for instance inductances which can be connected immediately across the slots instead of the strip and condensers or such inductances could be associated with condenser tuning if such is desired, the principles involved consisting in providing a resonant cavity behind a plurality of slots which are each tuned to a slightly different frequency to obtain a better overall band width through combining the wave form from three separately tuned slots.

What I claim is:

A wide band cavity type aerial consisting of box means having walls forming a plurality of independent resonant cavities, a pluralityof slots one opening from each said cavity through a wall thereof, a strip extending across the slots to feed the same signal to each of said slots, and a condenser across each slot to tune each of the slots so that each slot and its associated vcavity resonates at a Willoughby YAug. 24, 1,948

4 De Rosa et a1 Apr. 24, 1951 Rblet Apr. 4, 1953 Fales 2 July 20, 1954 FOREIGN PATENTS Great Britain T-' Apr. 8, 1948 France 2." Ian. 19, 1942 

